THE NERVOUS REGULATION OF THE HEART 161 



latent period of the sympathetic fibres when stimulated by themselves. 

 The inhibition apparently runs its course without being affected by the 

 simultaneous augmentor effect, which, lying latent until the end of the 

 inhibition, then bursts out and completes its own curve. It is not like 

 the passing of two waves through each other, but rather like the stopping 

 of one wave until the other has passed by. It seems as if augmentation 

 cannot develop itself in the presence of inhibition at least, until the 

 latter is nearly spent. Like a musical-box devised to play a series of 

 melodies in a fixed order, and from which a particular tune cannot be 

 obtained till those preceding it have been run through, the heart, in 

 some way or other, is arranged, in the presence of competing impulses 

 from its extrinsic nerves, to play the tune of inhibition before the tune 



Fig- 73. Frog's Heart. A, auricular, V, ventricular tracing. Ventricle beating very 

 feebly. Vagus stimulated (60 mm. between coils). Marked augmentation of 

 ventricular beat. 



of augmentation. In the frog, at any rate, the two processes can hardly 

 be- considered as antagonistic, in the sense that a definite amount of 

 augmentor excitation can overcome a definite amount of inhibitory 

 excitation. Nor is it the case that, when the heart is played upon at 

 the same time by impulses of both kinds, it pits them against each other 

 and strikes the balance accurately between them. It is possible, how- 

 ever, that when the inhibitory fibres are very weakly, and the augmentpr 

 fibres very strongly stimulated, the amount of inhibition may be some- 

 what diminished. In mammals, on the other hand, a true antagonism 

 seems to exist ; and stimulation of the inhibitory nerves is less effective 

 when the augmentors are excited at the same time. The cardiac nerves 

 affect not only the rate and force of the contraction, but also the con- 



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